The endoluminal introduction and deployment of a medical device such as a stent or stent graft into a patient is a well known procedure. The introducer assembly is typically in the form of a catheter assembly which includes at least guide wire, a guide wire catheter and an outer sheath. The medical device is carried at a distal end of the guide wire catheter and the assembly may also include a pusher element which is also carried on or is part of the guide wire catheter. It is advantageous to have a flexible distal end to the introducer to assist in its trackability within the vasculature of a patient. It is also advantageous for the distal tip of the introducer to have a dilating function so as to prepare the lumen for the passage of the larger sheath-covered part of the assembly. For this purpose it is generally considered best to have a specific dilator tip at the distal end of the introducer assembly, formed of a very flexible material. The implantable medical device is typically positioned just by the proximal end of the dilator tip and on a cannula or catheter which has a smaller outer diameter than the diameter of the dilator tip.
During deployment, the implantable medical device is expanded from the introducer until this fixes to the inner walls of the patient's lumen at the treatment site. Once deployed, the introducer is removed, typically by withdrawing the guide wire catheter through the lumen of the expanded medical device. The dilator tip also follows through the lumen of the medical device. This withdrawal operation generally occurs without complications. However, where the medical device is deployed in a curved vessel, such as in the aortic arch, it is possible for the distal end of the introducer assembly, particularly the dilator tip, to rub and pull against the internal surface of the medical device. The reason this occurs is that the introducer assembly will generally have a straight configuration, or at least much straighter than the curve of such a vessel, and as a result will tend to reside against or proximate the outer radial side of the lumen. Thus, when the introducer comes to be withdrawn, it will brush against this side of the vessel and the deployed medical device. In some circumstances this can cause damage or trauma to the vessel walls and or shift the device from the position in which it was deployed. There is also the risk of damage to the medical device. Any movement or damage to the device can lead to an abortive medical procedure.
WO-2006/117167 discloses an introducer for a self-expanding braided stent which includes a mechanism within the introducer assembly at its distal end for holding and controlling deployment of the stent.
U.S. Pat. No. 5,980,533, US-2006/0184226 and U.S. Pat. No. 7,331,985 disclose other designs of introducer assembly.